Current sensor

ABSTRACT

A current sensor including a magnetic detecting bridge circuit which is constituted of four magneto-resistance effect elements with a resistance value varied by application of an induced magnetic field from a current to be measured, and which has an output between two magneto-resistance effect elements. The four magneto-resistance effect elements have the same resistance change rate, and include a self-pinned type ferromagnetic fixed layer which is formed by anti-ferromagnetically coupling a first ferromagnetic film and a second ferromagnetic film via an antiparallel coupling film therebetween, a nonmagnetic intermediate layer, and a soft magnetic free layer. Magnetization directions of the ferromagnetic fixed layers of the two magneto-resistance effect elements providing the output are different from each other by 180°. The magnetic detecting bridge circuit has wiring symmetrical to a power supply point.

CLAIM OF PRIORITY

This application claims benefit of Japanese Patent Application No.2010-056154 filed on Mar. 12, 2010, which is hereby incorporated byreference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a current sensor using amagneto-resistance effect element (TMR element or GMR element).

2. Description of the Related Art

In an electric vehicle, a motor is driven by electricity generated by anengine, and the intensity of the current for driving the motor isdetected by, for example, a current sensor. The current sensor includesa magnetic core placed around a conductor and having a cutaway portion(core gap) formed at a portion thereof, and a magnetic detecting elementplaced in the core gap.

As the magnetic detecting element of the current sensor, amagneto-resistance effect element (GMR element, TMR element) including alaminate structure having a fixed magnetic layer with a fixedmagnetizing direction, a nonmagnetic layer, and a free magnetic layerwith a magnetizing direction varied with respect to an external magneticfield, or the like is used. Such a current sensor includes a full-bridgecircuit constituted by a magneto-resistance effect element and a fixedresistance element (Japanese Unexamined Patent Application PublicationNo. 2007-248054).

As the current sensor including a magnetic detecting bridge circuit(magnetic field detecting bridge circuit) constituted by themagneto-resistance effect element and the fixed resistance element, forexample, there is a magnetic balance current sensor shown in FIGS. 16and 17. The magnetic balance current sensor measures a current to bemeasured based on a current flowing in a feedback coil when the feedbackcoil is energized by a voltage difference obtained by a magneticdetecting bridge circuit 2, and then an induced magnetic field generatedby the current I to be measured which energizes a conductor 1, and acancelling magnetic field generated by the feedback coil are in anequilibrium state in which they are cancelled.

The magnetic detecting bridge circuit 2 of the current sensor shown inFIG. 16 includes one magneto-resistance effect element 201 and threefixed resistance elements 202 a to 202 c. In the magnetic detectingbridge circuit 2, a resistance value of the magneto-resistance effectelement 201 on a zero magnetic field is identical to a resistance valueof the fixed resistance elements 202 a to 202 c (Rcom). In addition, anoutput between the fixed resistance elements 202 b and 202 c is set toOut1, and an output between the magneto-resistance effect element 201and the fixed resistance element 202 a is set to Out2. In addition, aresistance value of the fixed resistance element 202 b is set to R1, aresistance value of the fixed resistance element 202 a is set to R2, aresistance value of the fixed resistance element 202 c is set to R3, anda resistance value of the magneto-resistance effect element 201 is setto R4.

When a resistance change amount of the magneto-resistance effect element201 according to the induced magnetic field generated from the current Ito be measured is ΔR, a midpoint potential difference (Out1 and Out2) ofthe bridge is obtained as follows:

Resistance between Vdd and Gnd1=R1+R3=2×R _(com)

Resistance between Vdd and Gnd2=

R2+(R4−ΔR)=2×R _(com) −ΔR

Potential of Out1=(R _(com))/(2×R _(com))×Vdd

Potential of Out2=(R _(com) −ΔR)/(2×R _(com) −ΔR)×Vdd

Potential difference between Out1 and Out2=

ΔR/{2×(2×R _(com) −ΔR)}×Vdd

The magnetic detecting bridge circuit 2 of the current sensor shown inFIG. 17 includes two magneto-resistance effect elements 201 a and 201 b,and two fixed resistance elements 202 a and 202 b. In the magneticdetecting bridge circuit 2, resistance values of the magneto-resistanceeffect elements 201 a and 201 b are equal to resistance values of thefixed resistance elements 202 a and 202 b (R_(com)). In addition,resistance change rates of the magneto-resistance effect elements 201 aand 201 b are equal to each other. Moreover, the output between themagneto-resistance effect element 201 b and the fixed resistance element202 b is set to Out1, and the output between the magneto-resistanceeffect element 201 a and the fixed resistance element 202 a is set toOut2. Further, a resistance value of the magneto-resistance effectelement 201 b is set to R1, a resistance value of the fixed resistanceelement 202 a is set to R2, a resistance value of the fixed resistanceelement 202 b is set to R3, and a resistance value of themagneto-resistance effect element 201 a is set to R4.

When a resistance change amount of the magneto-resistance effectelements 201 a and 201 b by the induced magnetic field generated fromthe current I to be measured is ΔR, a midpoint potential difference(Out1 and Out2) of the bridge is obtained as follows:

Resistance between Vdd and Gnd1=

(R1−ΔR)+R3=2×R _(com) −ΔR

Resistance between Vdd and Gnd2=

R2+(R4−ΔR)=2×R _(com) −ΔR

Potential of Out1=(R _(com))/(2×R _(com) −ΔR)×Vdd

Potential of Out2=(R _(com) −ΔR)/(2×R _(com) −ΔR)×Vdd

Potential difference between Out1 and Out2=

ΔR/(2×R _(com) −ΔR)×Vdd

However, in the configuration of the magnetic detecting bridge circuitshown in FIGS. 16 and 17, a term ΔR is contained in a denominator in theequation of the midpoint potential difference of the bridge. For thisreason, there is a problem that the output of the midpoint potentialdifference is not varied completely in proportion to the inducedmagnetic field which is generated by the current I to be measured, andthus the measurement accuracy is deteriorated.

SUMMARY OF THE INVENTION

Accordingly, the present invention is made to solve the above problemsof related arts, and an object of the present invention is to provide acurrent sensor in which an output of a midpoint potential difference isvaried in proportion to an induced magnetic field, thereby measuring acurrent with a high degree of accuracy.

According to an aspect of the present invention, there is provided acurrent sensor including: a magnetic detecting bridge circuit which isconstituted of four magneto-resistance effect elements with a resistancevalue varied by application of an induced magnetic field from a currentto be measured, and has an output between two magneto-resistance effectelements; wherein the four magneto-resistance effect elements have thesame resistance change rate, and include a self-pinned typeferromagnetic fixed layer which is formed by anti-ferromagneticallycoupling a first ferromagnetic film and a second ferromagnetic film viaan antiparallel coupling film therebetween, a nonmagnetic intermediatelayer, and a soft magnetic free layer, the magnetization directions ofthe ferromagnetic fixed layers of the two magneto-resistance effectelements providing the output are different from each other by 180°, andthe magnetic detecting bridge circuit has a wiring symmetrical to apower supply point.

With the configuration, since the magnetization directions of theself-pinned type ferromagnetic fixed layers in two magneto-resistanceeffect elements outputting the midpoint potential are different fromeach other by 180°, the output of the midpoint potential difference ischanged in proportion to the induced magnetic field which is generatedfrom the current to be measured, and it is possible to carry out thecurrent measurement with a high degree of accuracy. In addition, sincethe wiring is symmetrical to the power supply point in the magneticdetecting bridge circuit, there is no difference in the wiringresistances in the magnetic detecting bridge circuit, and it is possibleto carry out the current measurement with a higher degree of accuracy.

It is desirable that the current sensor according to the presentinvention further includes a feedback coil which is placed in thevicinity of the magneto-resistance effect element, and generates acancelling magnetic field for cancelling the induced magnetic field; anda magnetic shield which attenuates the induced magnetic field andenhances the cancelling magnetic field, wherein the current to bemeasured is measured based on a current flowing in the feedback coil atthe time of an equilibrium state in which the induced magnetic field andthe cancelling magnetic field are cancelled by energizing the feedbackcoil with a voltage difference obtained from the magnetic detectingbridge circuit.

In the current sensor according to the present invention, it isdesirable that in the four magneto-resistance effect elements, aplurality of belt-like elongated patterns are placed in such a way thatlongitudinal directions thereof are parallel with each other by againbending the elongated pattern, and the induced magnetic field and thecancelling magnetic field are applied in a direction perpendicular tothe longitudinal direction.

In the current sensor according to the present invention, it isdesirable that the magnetic detecting bridge circuit measures thecurrent to be measured by the outputs of the four magneto-resistanceeffect elements which are in proportion to the induced magnetic field.

In the current sensor according to the present invention, it isdesirable that the first ferromagnetic film is made of a CoFe alloycontaining Fe of 40 atomic percent to 80 atomic percent, and the secondferromagnetic film is made of a CoFe alloy containing Fe of 0 atomicpercent to 40 atomic percent.

In the current sensor according to the present invention, it isdesirable that the magnetic shield is made of a high permeabilitymaterial selected from a group consisting of an amorphous magneticmaterial, a permalloy-based magnetic material, and an iron-basedmicrocrystalline material.

With the present invention, the current sensor includes the magneticdetecting bridge circuit which is constituted of four magneto-resistanceeffect elements with the resistance value varied by application of theinduced magnetic field from the current to be measured, and which hasoutput between two magneto-resistance effect elements. The fourmagneto-resistance effect elements have the same resistance change rate,and includes the self-pinned type ferromagnetic fixed layer which isformed by anti-ferromagnetically coupling the first ferromagnetic filmand the second ferromagnetic film via the antiparallel coupling filmtherebetween, the nonmagnetic intermediate layer, and the soft magneticfree layer. The magnetization directions of the ferromagnetic fixedlayers of the two magneto-resistance effect elements providing theoutput are different from each other by 180°, and the magnetic detectingbridge circuit has a wiring symmetrical to a power supply point. As aresult, the output of the midpoint potential difference is changed inproportion to the induced magnetic field which is generated from thecurrent to be measured, and there is no difference in the wiringresistances in the magnetic detecting bridge circuit. Therefore, it ispossible to carry out the current measurement with a high degree ofaccuracy.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram illustrating a magnetic balance current sensoraccording to an embodiment of the present invention.

FIG. 2 is a diagram illustrating a magnetic balance current sensoraccording to an embodiment of the present invention.

FIG. 3 is a cross-sectional view illustrating a magnetic balance currentsensor shown in FIG. 1.

FIG. 4 is a diagram illustrating a magnetic detecting bridge circuit ina magnetic balance current sensor according to an embodiment of thepresent invention.

FIG. 5A is a diagram illustrating a wiring pattern of a magneticdetecting bridge circuit in a magnetic balance current sensor accordingto an embodiment of the present invention.

FIG. 5B is a cross-sectional view taken along the line VB-VB in FIG. 5A.

FIG. 6A is a diagram illustrating a wiring pattern of a magneticdetecting bridge circuit in a magnetic balance current sensor accordingto an embodiment of the present invention.

FIG. 6B is a cross-sectional view taken along the line VIB-VIB in FIG.6A.

FIG. 7A is a diagram illustrating a wiring pattern of a magneticdetecting bridge circuit in a magnetic balance current sensor accordingto an embodiment of the present invention.

FIG. 7B is a cross-sectional view taken along the line VIIB-VIIB in FIG.7A.

FIG. 8 is a diagram illustrating a relationship between a midpointpotential difference and an induced magnetic field generated from acurrent to be measured.

FIG. 9 is a diagram illustrating a wiring pattern of a magneticdetecting bridge circuit in a magnetic balance current sensor accordingto an embodiment of the present invention.

FIGS. 10A to 10C are diagrams illustrating a method of manufacturing amagneto-resistance effect element in a current sensor according to anembodiment of the present invention.

FIGS. 11A to 11C are diagrams illustrating a method of manufacturing amagneto-resistance effect element in a current sensor according to anembodiment of the present invention.

FIG. 12 is a diagram illustrating a magnetic proportional current sensoraccording to an embodiment of the present invention.

FIG. 13 is a diagram illustrating a magnetic proportional current sensoraccording to an embodiment of the present invention.

FIG. 14 is a cross-sectional view illustrating the magnetic proportionalcurrent sensor in FIG. 12.

FIG. 15 is a diagram illustrating a magnetic detecting bridge circuit ina magnetic proportional current sensor according to an embodiment of thepresent invention.

FIG. 16 is a diagram illustrating a magnetic detecting bridge circuit ina magnetic balance current sensor according to the related art.

FIG. 17 is a diagram illustrating a magnetic detecting bridge circuit ina magnetic balance current sensor according to the related art.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments of the present invention will be now described in detailwith reference to the accompanying drawings. First, a case where acurrent sensor according to the present invention is a magnetic balancecurrent sensor will be described.

FIGS. 1 and 2 are diagrams illustrating a magnetic balance currentsensor according to an embodiment of the present invention. The magneticbalance current sensor shown in FIGS. 1 and 2 is installed adjacent to aconductor 11 through which a current I to be measured flows. Themagnetic balance current sensor includes a feedback circuit 12 forinducing a magnetic field (cancelling magnetic field) for cancelling aninduced magnetic field generated from the current I to be measured whichflows in the conductor 11. The feedback circuit 12 has a feedback coil121 wound in a direction for cancelling a magnetic field generated fromthe current I to be measured, and four magneto-resistance effectelements 122 a to 122 d.

The feedback coil 121 is constituted of a planar coil. Since theconfiguration does not have a magnetic core, the feedback coil can bemade at low cost. In addition, as compared with a case of a toroidalcoil, it is possible to prevent the cancelling magnetic field, which isgenerated from the feedback coil, from extensively spreading, and toprevent it from impacting on peripheral circuits. In addition, ascompared with the case of the toroidal coil, if the current to bemeasured is an alternating current, the control of the cancellingmagnetic field by the feedback coil is easy, and a current flowing forthe control is not particularly increased. These effects become greateras the current to be measured, which is an alternating current, becomesa high frequency. In the case where the feedback coil 121 is constitutedof the planar coil, it is desirable that the planar coil is providedsuch that both the induced magnetic field and the cancelling magneticfield are generated in a plane which is parallel with a forming surfaceof the planar coil.

The resistance values of the magneto-resistance effect elements 122 a to122 d are varied by application of the induced magnetic field from thecurrent I to be measured. The four magneto-resistance effect elements122 a to 122 d constitute a magnetic detecting bridge circuit. Amagnetic balance current sensor with high sensitivity can be achieved byusing the magnetic detecting bridge circuit having themagneto-resistance effect elements.

The magnetic detecting bridge circuit has two outputs for inducing avoltage difference in accordance with the induced magnetic fieldgenerated by the current I to be measured. In the magnetic detectingbridge circuit shown in FIG. 2, a power source Vdd is connected to aconnection point between the magneto-resistance effect element 122 b andthe magneto-resistance effect element 122 c, and a ground (GND) isconnected to a connection point between the magneto-resistance effectelement 122 a and the magneto-resistance effect element 122 d. Inaddition, in the magnetic detecting bridge circuit, one output (Out1) istaken from the connection point between the magneto-resistance effectelements 122 a and 122 b, and the other output (Out2) is taken from theconnection point between magneto-resistance effect elements 122 c and122 d. The two outputs are amplified by an amplifier 124, and then areapplied to the feedback coil 121 as a current (feedback current). Thefeedback current corresponds to a voltage difference in accordance withthe induced magnetic field. At that time, the cancelling magnetic fieldfor cancelling the induced magnetic field is generated from the feedbackcoil 121. The current to be measured is measured by a detection unit(detection resistor R) based on the current flowing in the feedback coil121 at the time of an equilibrium state in which the induced magneticfield and the cancelling magnetic field are cancelled.

FIG. 3 is a cross-sectional view illustrating the magnetic balancecurrent sensor shown in FIG. 1. As shown in FIG. 3, in the magneticbalance current sensor according to the embodiment, the feedback coil,the magnetic shield, and the magnetic detecting bridge circuit areformed on the same substrate 21. In the configuration shown in FIG. 3,the feedback coil is placed between the magnetic shield and the magneticdetecting bridge circuit, and the magnetic shield is placed at a sidenear to the current I to be measured. That is, the magnetic shield, thefeedback coil, and the magneto-resistance effect element are placed inorder from the side near the conductor 11. In this way, themagneto-resistance effect element can be the farthest away from theconductor 11, and the induced magnetic field applied to themagneto-resistance effect element from the current I to be measured canbe reduced. Further, since the magnetic shield can be the nearest theconductor 11, the attenuation effect of the induced magnetic field canbe further improved. Accordingly, the cancelling magnetic field from thefeedback coil can be reduced.

The layer configuration shown in FIG. 3 will be described in detail. Inthe magnetic balance current sensor shown in FIG. 3, a thermal siliconoxide film 22 serving as an insulating layer is formed on the substrate21. An aluminum oxide film 23 is formed on the thermal silicon oxidefilm 22. For example, the aluminum oxide film 23 can be formed as a filmby a method such as sputtering or the like. In addition, a siliconsubstrate or the like is used as the substrate 21.

The magneto-resistance effect elements 122 a to 122 d are formed on thealuminum oxide film 23 to form a magnetic detecting bridge circuit. Asthe magneto-resistance effect elements 122 a to 122 d, a TMR element(tunnel magneto-resistance effect element), a GMR element (giantmagneto-resistance effect element), or the like can be used. The filmconfiguration of the magneto-resistance effect element for using in themagnetic balance current sensor according to the present invention willbe described below.

As the magneto-resistance effect element, a GMR element having ameandering shape is desirable, as shown in the enlarged view of FIG. 2,in which a plurality of belt-like elongated patterns (stripes) areplaced in such a way that longitudinal directions thereof are parallelwith each other by being folded back. In the meandering shape, asensitivity axis direction (Pin direction) is a direction (widthwisedirection of the stripes) perpendicular to the longitudinal direction(longitudinal direction of the stripes) of the elongated pattern. In themeandering shape, the induced magnetic field and the cancelling magneticfield are applied in the direction perpendicular to a longitudinaldirection of the stripe.

Considering the linearity in the meandering shape, it is desirable thatthe width of the meandering shape in a Pin direction is 1 μm to 10 μm.In this instance, considering the linearity, it is desirable that thelongitudinal direction is perpendicular to the direction of the inducedmagnetic field and the direction of the cancelling magnetic field. Withthe meandering shape, it is possible to achieve the output of themagneto-resistance effect element with fewer terminals (two terminals)than Hall elements.

In addition, an electrode 24 is formed on the aluminum oxide layer 23.The electrode 24 may be formed by photolithography and etching after anelectrode material is formed as a film.

On the aluminum oxide layer 23 formed with the magneto-resistance effectelements 122 a to 122 d and the electrode 24, a polyimide layer 25 isformed as an insulating layer. The polyimide layer 25 may be formed byapplying and curing a polyimide material.

A silicon oxide film 27 is formed on the polyimide layer 25. The siliconoxide film 27 is formed as a film by, for example, sputtering or thelike.

The feedback coil 121 is formed on the silicon oxide film 27. Thefeedback coil 121 may be formed by photolithography and etching after acoil material is formed as a film. Alternatively, the feedback coil 121may be formed by photolithography and plating after a base material isformed as a film.

In addition, a coil electrode 28 is formed on the silicon oxide film 27in the vicinity of the feedback coil 121. The coil electrode 28 may beformed by photolithography and etching after an electrode material isformed as a film.

On the silicon oxide layer 27 formed with the feedback coil 121 and thecoil electrode 28, a polyimide layer 29 is formed as an insulatinglayer. The polyimide layer 29 may be formed by applying and curing apolyimide material.

A magnetic shield 30 is formed on the polyimide layer 29. Theconfiguration material of the magnetic shield 30 can use a highpermeability material such as an amorphous magnetic material, apermalloy-based magnetic material, or an iron-based microcrystallinematerial.

A silicon oxide layer 31 is formed on the polyimide layer 29. Thesilicon oxide layer 31 may be formed as a film by a method such as, forexample, sputtering. Contact holes are formed in predetermined regionsof the polyimide layer 29 and the silicon oxide layer 31 (a region ofthe coil electrode 28 and a region of the electrode 24), and electrodepads 32 and 26 are formed in the contact holes. The contact holes areformed by photolithography and etching. The electrode pads 32 and 26 maybe formed by photolithography and plating after the electrode materialis formed as a film.

In the magnetic balance current sensor including the above-describedconfiguration, as shown in FIG. 3, the magneto-resistance effect elementreceives the induced magnetic field A generated from the current I to bemeasured, and then the induced magnetic field is fed back to generatethe cancelling magnetic field B from the feedback coil 121. Two magneticfields (the induced magnetic field A and the cancelling magnetic fieldB) are appropriately adjusted in such a way that the magnetic fields arecancelled to let a magnetic field applied to the magneto-resistanceeffect elements 122 a to 122 d be zero.

The magnetic balance current sensor according to the present inventionincludes the magnetic shield 30 in the vicinity of the feedback coil121, as shown in FIG. 3. The magnetic shield 30 can attenuate theinduced magnetic field generated from the current I to be measured andapplied to the magneto-resistance effect elements 122 a to 122 d (thedirection of the induced magnetic field A and the direction of thecancelling magnetic field B are opposite directions in themagneto-resistance effect elements 122 a to 122 d), and enhance thecancelling magnetic field B from the feedback coil 121 (the direction ofthe induced magnetic field A and the direction of the cancellingmagnetic field B are the same direction in the magnetic shield 30).Accordingly, since the magnetic shield 30 functions as a magnetic yoke,the current flowing in the feedback coil 121 can be reduced, and thusreduced power consumption can be achieved. In addition, the effect ofthe external magnetic field can be reduced by the magnetic shield 30.

The magnetic balance current sensor including the above-describedconfiguration utilizes the magneto-resistance effect element as themagnetic detecting element, in particular, the magnetic detecting bridgecircuit having the GMR element or the TMR element, so that a magneticbalance current sensor having high sensitivity can be achieved. Inaddition, in the magnetic balance current sensor, the magnetic detectingbridge circuit is constituted of four magneto-resistance effect elementswith the same film configuration. Further, in the magnetic balancecurrent sensor including the above-described configuration, since thefeedback coil 121, the magnetic shield 30, and the magnetic fielddetecting bridge are formed on the same substrate, the miniaturizationthereof can be achieved. Moreover, since the magnetic balance currentsensor does not include the magnetic core, miniaturization and costreduction can be achieved.

The film configuration of the magneto-resistance effect element used inthe present invention is shown, for example, in FIG. 10A. That is, themagneto-resistance effect element includes the laminate structureprovided on the substrate 41, as shown in FIG. 10A. In addition, asshown in FIG. 10A, other than the magneto-resistance effect element, abase layer or the like is not shown on the substrate 41, in order tofacilitate the description. The magneto-resistance effect elementincludes a seed layer 42 a, a first ferromagnetic film 43 a, anantiparallel coupling film 44 a, a second ferromagnetic film 45 a, anon-magnetic intermediate layer 46 a, soft magnetic free layers (freemagnetic layer) 47 a and 48 a, and a protective layer 49 a.

The seed layer 42 a is made of NiFeCr, Cr or the like. The protectivelayer 49 a is made of Ta or the like. In addition, in the laminatestructure, a base layer made of a nonmagnetic material, such as any oneelement of, for example, Ta, Hf, Nb, Zr, Ti, Mo, and W, may be providedbetween the substrate 41 and the seed layer 42 a.

In the magneto-resistance effect element, the first ferromagnetic film43 a and the second ferromagnetic film 45 a are coupled in anantiferromagnetic manner via the antiparallel coupling film 44 atherebetween, thereby forming a so-called ferromagnetic fixed layer(SFP: Synthetic Ferri Pinned layer) of a self-pinned type.

In the ferromagnetic fixed layer, as the thickness of the antiparallelcoupling film 44 a is set to 0.3 nm to 0.45 nm, or 0.75 nm to 0.95 nm, astrong antiferromagnetic coupling is achieved between the firstferromagnetic film 43 a and the second ferromagnetic film 45 a.

In addition, the magnetization amount (Ms·t) of the first ferromagneticfilm 43 a and the magnetization amount (Ms·t) of the secondferromagnetic film 45 a are substantially equal to each other. That is,the difference in the magnetization amount between the firstferromagnetic film 43 a and the second ferromagnetic film 45 a issubstantially zero. For this reason, the effective anisotropic magneticfield of the SFP layer is large. Accordingly, even though theantiferromagnetic material is not used, magnetization stability of theferromagnetic fixed layer (Pinned layer) can be sufficiently ensured.Supposing that the film thickness of the first ferromagnetic film is t1,the film thickness of the second ferromagnetic film is t2, andmagnetization and induced magnetic anisotropic constants per unit volumeof both layers are Ms and K, the effective anisotropic magnetic field ofthe SFP layer is represented by Equation 1 below:

eff HK=2(K·t1+K·t2)/(Ms·t1−Ms·t2)  Equation 1

Accordingly, the magneto-resistance effect element used in the magneticbalance current sensor according to the present invention includes alayer structure with no antiferromagnetic layer.

A Curie temperature (Tc) of the first ferromagnetic film 43 a and aCurie temperature (Tc) of the second ferromagnetic film 45 a aresubstantially equal to each other. In this way, the difference in themagnetization amounts (Ms·t) of the two films 43 a and 45 a under a hotenvironment becomes zero, and thus the high magnetization stability canbe maintained.

It is desirable that the first ferromagnetic film 43 a is made of a CoFealloy containing Fe of 40 atomic percent to 80 atomic percent. Thereason is that the CoFe alloy of the composition range has a highcoercive force, and maintains the magnetization reliably with respect tothe external magnetic field. In addition, it is desirable that thesecond ferromagnetic film 45 a is made of a CoFe alloy containing Fe of0 atomic percent to 40 atomic percent. The reason is that the CoFe alloyof the composition range has a low coercive force, and is easilymagnetized in an antiparallel direction (180° different direction) withrespect to a preferential magnetization direction of the firstferromagnetic film 43 a. As a result, it is possible to further increaseHk. In addition, by limiting the second ferromagnetic film 45 a in thiscomposition range, the resistance change rate of the magneto-resistanceeffect element can be increased.

It is desirable that during film formation, a magnetic field is appliedto the first ferromagnetic film 43 a and the second ferromagnetic film45 a in the widthwise direction of stripes of the meandering shape, andafter film formation, the induced magnetic anisotropy is applied to thefirst ferromagnetic film 43 a and the second ferromagnetic film 45 a. Inthis way, both the first ferromagnetic film 43 a and the secondferromagnetic film 45 a are magnetized antiparallel to the widthwisedirection of the stripes. In addition, since the magnetization directionof the first ferromagnetic film 43 a and the second ferromagnetic film45 a is determined by the applying direction of the magnetic field atthe time of film formation of the first ferromagnetic film 43 a, it ispossible to form the plurality of magneto-resistance effect elementshaving the ferromagnetic fixed layer of different magnetizationdirection on the same substrate by changing the applying direction ofthe magnetic field at the time of film formation of the firstferromagnetic film 43 a.

The antiparallel coupling film 44 a of the ferromagnetic fixed layer ismade of Ru or the like. In addition, the soft magnetic free layers (freelayer) 47 a and 48 a are made of a magnetic material such as a CoFealloy, a NiFe alloy, a CoFeNi alloy or the like. Further, thenonmagnetic intermediate layer 46 a is made of Cu or the like. Moreover,it is desirable that during film formation, a magnetic field is appliedto the soft magnetic free layers 47 a and 48 a in the widthwisedirection of the stripes of the meandering shape, and after filmformation, the induced magnetic anisotropy is applied to the softmagnetic free layers 47 a and 48 a. In this way, in themagneto-resistance effect element, the resistance is linearly changedwith respect to an external magnetic field (magnetic field from thecurrent to be measured) of the widthwise direction of the stripes, sothat hysteresis can be reduced. The magneto-resistance effect elementincludes a spin valve configuration with the ferromagnetic fixed layer,the nonmagnetic intermediate layer, and the soft magnetic free layer.

An example of the film configuration of the magneto-resistance effectelement for use in the magnetic balance current sensor according to thepresent invention includes, for example, NiFeCr (seed layer: 5 nm),Fe70Co30 (first ferromagnetic film: 1.65 nm), Ru (antiparallel couplingfilm: 0.4 nm), Co90Fe10 (second ferromagnetic film: 2 nm), Cu(nonmagnetic intermediate layer: 2.2 nm), Co90Fe10 (soft magnetic freelayer: 1 nm), NiFe (soft magnetic free layer: 7 nm), and Ta (protectivelayer: 5 nm).

In the magnetic balance current sensor according to the presentinvention, as shown in FIG. 4, the magnetization directions(magnetization direction of the second ferromagnetic film: Pin2) of twomagneto-resistance effect elements 122 b and 122 d outputting themidpoint potential (Out1) are different from each other by 180°(antiparallel), and the magnetization directions (magnetizationdirection of the second ferromagnetic film: Pin2) of twomagneto-resistance effect elements 122 a and 122 c outputting themidpoint potential (Out2) are different from each other by 180°(antiparallel). In addition, the resistance change rate of the fourmagneto-resistance effect elements 122 a to 122 d is equal to eachother. In a case where the angle of the magnetic field applied to theferromagnetic fixed layer is equal, it is desirable that themagneto-resistance effect elements 122 a to 122 d represent the sameresistance change rate at the same magnetic strength.

In the magnetic balance current sensor including the fourmagneto-resistance effect elements 122 a to 122 d placed as describedabove, the current to be measured is measured by applying the cancellingmagnetic field to the magneto-resistance effect element from thefeedback coil 121 so that the voltage difference between two outputsOut1 and Out2 of the magnetic detecting bridge circuit becomes zero, anddetecting the value of the current flowing in the feedback coil 121 atthat time. At this time, among the four magneto-resistance effectelements 122 a to 122 d, the magneto-resistance effect elements 122 aand 122 b serve as the magneto-resistance effect element, and themagneto-resistance effect elements 122 c and 122 d serve as the fixedresistance element.

As shown in FIG. 4, if the current I to be measured flows in thedirection of the arrow, the induced magnetic field A and the cancellingmagnetic field B are respectively applied to the four magneto-resistanceeffect elements 122 a to 122 d. At that time, when the compositemagnetic field strength of the induced magnetic field and the cancellingmagnetic field generated from the current to be measured becomes zero,the midpoint potential difference of the magnetic detecting bridgecircuit becomes zero.

In the magnetic detecting bridge circuit, the resistance values of themagneto-resistance effect elements 122 a to 122 d in a zero magneticfield are equal to each other (Rcom). In addition, the resistance changerates of the magneto-resistance effect elements 122 a to 122 d are equalto each other. The output between the magneto-resistance effect elements122 b and 122 d is set to Out1, and the output between themagneto-resistance effect elements 122 a and 122 c is set to Out2.Moreover, a resistance value of the magneto-resistance effect element122 b is set to R1, a resistance value of the magneto-resistance effectelement 122 c is set to R2, a resistance value of the magneto-resistanceeffect element 122 d is set to R3, and a resistance value of themagneto-resistance effect element 122 a is set to R4.

When the resistance change amount of the magneto-resistance effectelements 122 a to 122 d according to the induced magnetic fieldgenerated from the current I to be measured is ΔR, a midpoint potentialdifference (Out1 and Out2) of the bridge is obtained as follows:

Resistance between Vdd and Gnd1=

(R1−ΔR)+(R3+ΔR)=R1+R3=2×R _(com)

Resistance between Vdd and Gnd2=

(R2++ΔR)+(R4−ΔR)=R2+R4=2×R _(com)

Potential of Out1=(R3+ΔR)/(R1+R3)×Vdd

=(R _(com) +ΔR)/(2×R _(com))×Vdd

Potential of Out2=(R4−ΔR)/(R2+R4)×Vdd

=(R _(com) −ΔR)/(2×R _(com))×Vdd

Potential difference between Out1 and Out2=

(2×ΔR)/(2×R _(com))×Vdd

=ΔR/R _(com) ×Vdd

As described above, in the magnetic balance current sensor according tothe present invention, a term ΔR is not contained in a denominator inthe equation of the midpoint potential difference of the bridge. Forthis reason, the output of the midpoint potential difference is variedin proportion to the induced magnetic field which is generated by thecurrent I to be measured. As a result, it is possible to carry out thecurrent measurement with a high degree of accuracy.

FIG. 5A is a diagram illustrating a wiring pattern of the magneticdetecting bridge circuit in the magnetic balance current sensoraccording to an embodiment of the present invention. FIG. 5B is across-sectional view taken along the line VB-VB in FIG. 5A. The magneticdetecting bridge circuit of the magnetic balance current sensoraccording to the present invention includes wiring symmetrical to apower supply point, as shown in FIG. 5A. The magneto-resistance effectelements 122 a to 122 d are formed in the extending direction(conduction direction of the feedback current) of the coil pattern ofthe feedback coil 121 and the stripe longitudinal direction ofmeandering shape thereof, as shown in FIG. 5A. The feedback coil isinstalled on the magneto-resistance effect element, as shown in FIG. 5B.

In addition, a wiring pattern 60 is formed to be connected to themagneto-resistance effect elements 122 a to 122 d and a power supplypoint (Vdd) or Gnd. The wiring pattern 60 is symmetrical to the powersupply point. In this way, since the lengths of the wiring at both sidesof the power supply point are substantially equal to each other, thereis no difference in the wiring resistances at both sides of the powersupply point. As a result, since there is no misalignment of themidpoint potential caused by the difference in wiring resistances, it ispossible to carry out the current measurement with a high degree ofaccuracy.

FIG. 6A is a diagram illustrating a wiring pattern of the magneticdetecting bridge circuit in the magnetic balance current sensoraccording to an embodiment of the present invention. FIG. 6B is across-sectional view taken along the line VIB-VIB in FIG. 6A. Themagnetic detecting bridge circuit of the magnetic balance current sensoraccording to the present invention includes wiring symmetrical to apower supply point, as shown in FIG. 6A. The magneto-resistance effectelements 122 a to 122 d are formed in the extending direction(conduction direction of the feedback current) of a spiral pattern 61 ofthe feedback coil 121 and the longitudinal direction of the stripes ofthe meandering shape thereof, as shown in FIG. 6A. The spiral pattern 61of the feedback coil 121 is installed on the magneto-resistance effectelement, as shown in FIG. 6B.

In addition, a wiring pattern 60 is formed to be connected to themagneto-resistance effect elements 122 a to 122 d and a power supplypoint (Vdd) or Gnd. The wiring pattern 60 is symmetrical to the powersupply point. In this way, since the lengths of the wiring at both sidesof the power supply point are substantially equal to each other, thereis no difference in the wiring resistances at both sides of the powersupply point. As a result, since there is no misalignment of themidpoint potential caused by the difference in wiring resistances, it ispossible to carry out the current measurement with a high degree ofaccuracy. Further, since a region with no magneto-resistance effectelement can be omitted in the feedback coil 121 by using the spiralpattern 61, it is possible to decrease the area of the feedback coil.

FIG. 7A is a diagram illustrating a wiring pattern of a magneticdetecting bridge circuit in the magnetic balance current sensoraccording to an embodiment of the present invention. FIG. 7B is across-sectional view taken along the line VIIB-VIIB in FIG. 7A. Themagnetic detecting bridge circuit of the magnetic balance current sensoraccording to the present invention includes wiring symmetrical to apower supply point, as shown in FIG. 7A. The magneto-resistance effectelements 122 a to 122 d are formed in the extending direction(conduction direction of the feedback current) of the feedback coil 121and the longitudinal direction of the stripes of the meandering shapethereof, as shown in FIG. 7A. The feedback coil 121 is installed on twomagneto-resistance effect elements 122 a and 122 d, and the feedbackcoil 121 is installed below two magneto-resistance effect elements 122 band 122 c, as shown in FIG. 7B.

In addition, a wiring pattern 60 is formed to be connected to themagneto-resistance effect elements 122 a to 122 d and a power supplypoint (Vdd) or Gnd. The wiring pattern 60 is symmetrical to the powersupply point. In this way, since the lengths of the wiring at both sidesof the power supply point are substantially equal to each other, thereis no difference in the wiring resistances at both sides of the powersupply point. As a result, since there is no misalignment of themidpoint potential caused by the difference in wiring resistances, it ispossible to carry out the current measurement with a high degree ofaccuracy. Further, by using the coil pattern shown in FIG. 7, fourmagneto-resistance effect elements are not arranged in parallel, but twomagneto-resistance effect elements are arranged in parallel, so that themagneto-resistance effect element can be provided in two extendingregions of the feedback coil 121. As a result, it is possible to shortenthe length of the magnetic detecting bridge circuit in the widthwisedirection (conduction direction of the feedback current).

The magnetic balance current sensor using the four magneto-resistanceeffect elements can also be made using a type of magneto-resistanceeffect element which fixes the magnetization of a fixed magnetic layeras an antiferromagnetic film. In this instance, in order to make theexchange coupling direction of a fixed magnetic layer (Pinned layer)which is one of two magneto-resistance effect elements be antiparallelto the exchange coupling direction of the fixed magnetic layer of theother, it is necessary to apply laser lock annealing or install amagnetic field applying coil adjacent to the magneto-resistance effectelement. Such a method can be applied to a case where themagneto-resistance effect element manufactures a sensor or devicepositioned near a topmost surface of a chip, but it cannot be applied tothe manufacture of a device with a thick organic insulating film, athick feedback coil, or a thick magnetic shield film provided on themagneto-resistance effect element, like the magnetic balance currentsensor according to the present invention. For this reason, theconfiguration of the present invention is particularly useful for themagnetic balance current sensor according to the present invention.

In the case where the magnetic detecting bridge circuit and the feedbackcoil are integrally formed on the same substrate, like the magneticbalance current sensor according to the present invention, since both ofthem should be completely insulated from each other, both the magneticdetecting bridge circuit and the feedback coil are separated by anorganic insulating film such as polyimide film. The organic insulatingfilm is generally formed by applying it with a spin coater or the like,and then heating it at 200° C. or more. Since the organic insulatingfilm is formed during a subsequent process of forming the magneticdetecting bridge circuit, the magneto-resistance effect element is alsoheated. In the process of manufacturing a type of magneto-resistanceeffect element which fixes the magnetization of the fixed magnetic layeras an antiferromagnetic film, it is necessary to perform heating whileapplying the magnetic field, so as not to deteriorate thecharacteristics of the fixed magnetic layer due to thermal hysteresis atthe process of forming the organic insulating film. In the magneticbalance current sensor according to the present invention, since theantiferromagnetic film is not used, it is possible to maintain thecharacteristics of the fixed magnetic layer, even without carrying out aheating process while applying the magnetic field. Accordingly, thedeterioration in hysteresis of the soft magnetic free layer can besuppressed.

In addition, since the magneto-resistance effect element of the magneticbalance current sensor according to the present invention does notcontain an antiferromagnetic material, it is possible to suppress amaterial cost or manufacturing cost.

An embodiment for clearly explaining the effects of the presentinvention will be described. A relationship between the induced magneticfield (magnetic field of the current to be measured) generated from thecurrent to be measured and the midpoint potential difference of themagnetic detecting bridge circuit was tested on the magnetic balancecurrent sensor having the magnetic detecting bridge circuit shown inFIG. 4. The result is shown in FIG. 8. In addition, a relationshipbetween the induced magnetic field (magnetic field of the current to bemeasured) generated from the current to be measured and the midpointpotential difference of the magnetic detecting bridge circuit was alsotested on the magnetic balance current sensor (the related art (GMRx1))having the magnetic detecting bridge circuit shown in FIG. 16, and themagnetic balance current sensor (the related art (GMRx2)) having themagnetic detecting bridge circuit shown in FIG. 17. The result is shownin FIG. 8.

As can be seen from FIG. 8, as the midpoint potential difference ischanged in the shape of a straight line with respect to the inducedmagnetic field generated from the current to be measured, the magneticbalance current sensor (the invention) according to the presentinvention can carry out the current measurement with a high degree ofaccuracy. In particular, since the four magneto-resistance effectelements are used, it is possible to achieve a current sensor with highsensitivity. Meanwhile, as the midpoint potential difference is changedin the shape of a curved line with respect to the induced magnetic fieldgenerated from the current to be measured, the magnetic balance currentsensors (the related art (GMRx1) and the related art (GMRx2)) accordingto the related arts cannot carry out the current measurement with a highdegree of accuracy.

The present invention can be equally applied to a magnetic proportionalcurrent sensor for measuring the current to be measured by the output oftwo magneto-resistance effect elements in proportion to the inducedmagnetic field, as well as the magnetic balance current sensor. As shownin FIG. 9, the magnetic proportional current sensor includes aconfiguration similar to the configuration shown in FIG. 5A, except forthe feedback coil. In addition, the magneto-resistance effect element ofthe magnetic proportional current sensor has four magneto-resistanceeffect elements 122 a to 122 d, as shown in FIG. 9, and, similar to theconfiguration shown in FIGS. 5 to 7, has a wiring symmetrical to a powersupply point. Further, the magnetization directions (magnetizationdirection of the second ferromagnetic film: Pin2) of twomagneto-resistance effect elements 122 b and 122 d outputting themidpoint potential (Out1) are different from each other by 180°(antiparallel), and the magnetization directions (magnetizationdirection of the second ferromagnetic film: Pin2) of twomagneto-resistance effect elements 122 a and 122 c outputting themidpoint potential (Out2) are different from each other by 180°(antiparallel). In addition, the resistance change rate of the fourmagneto-resistance effect elements 122 a to 122 d is equal to eachother.

The case where the current sensor according to the present invention isthe magnetic proportional current sensor will now be described indetail.

FIGS. 12 and 13 are diagrams illustrating a magnetic proportionalcurrent sensor according to an embodiment of the present invention. Themagnetic proportional current sensor shown in FIGS. 12 and 13 isinstalled adjacent to a conductor 11 through which a current I to bemeasured flows. The magnetic proportional current sensor includes amagnetic field detecting bridge circuit (magnetic detecting bridgecircuit) 13 for detecting the induced magnetic field generated from thecurrent I to be measured which flows in the conductor 11. The magneticfield detecting bridge circuit 13 has four magneto-resistance effectelements 122 a to 122 d of which the resistance value is varied byapplication of the induced magnetic field from the current I to bemeasured.

The magnetic field detecting bridge circuit 13 has two outputs forinducing a voltage difference in accordance with the induced magneticfield generated by the current I to be measured. In the magnetic fielddetecting bridge circuit 13 shown in FIG. 13, a power source Vdd isconnected to a connection point between the magneto-resistance effectelement 122 b and the magneto-resistance effect element 122 c, and aground (GND) is connected to a connection point between themagneto-resistance effect element 122 a and the magneto-resistanceeffect element 122 d. In addition, in the magnetic field detectingbridge circuit 13, one output (Out1) is taken from the connection pointbetween the magneto-resistance effect elements 122 a and 122 b, and theother output (Out2) is taken from the connection point betweenmagneto-resistance effect elements 122 c and 122 d. The magneticproportional current sensor calculates the current I to be measured fromthe voltage difference between two outputs.

FIG. 14 is a cross-sectional view illustrating the magnetic proportionalcurrent sensor shown in FIG. 12. As shown in FIG. 14, in the magneticproportional current sensor according to the embodiment, the magneticshield and the magnetic field detecting bridge circuit are formed on thesame substrate 21. In the configuration shown in FIG. 14, the magneticshield is placed at a side near to the current I to be measured. Thatis, the magnetic shield and the magneto-resistance effect element areplaced in order from the side near the conductor 11. In this way, themagneto-resistance effect element can be farthest away from theconductor 11, and the induced magnetic field applied to themagneto-resistance effect element from the current I to be measured canbe reduced. Accordingly, the current measurement in the wide range ispossible.

The layer configuration shown in FIG. 14 will be described in detail. Inthe magnetic proportional current sensor shown in FIG. 14, a thermalsilicon oxide film 22 serving as an insulating layer is formed on thesubstrate 21. An aluminum oxide film 23 is formed on the thermal siliconoxide film 22. For example, the aluminum oxide film 23 can be formed asa film by a method such as sputtering or the like. In addition, asilicon substrate or the like is used as the substrate 21.

The magneto-resistance effect elements 122 a to 122 d are formed on thealuminum oxide film 23 to form a magnetic field detecting bridgecircuit. As the magneto-resistance effect elements 122 a to 122 d, a TMRelement (tunnel magneto-resistance effect element), a GMR element (giantmagneto-resistance effect element), or the like can be used. The filmconfiguration of the magneto-resistance effect element for use in themagnetic proportional current sensor according to the present inventionis shown, for example, in FIG. 10. The detailed configuration isdescribed above, and thus the description thereof will be omittedherein.

As the magneto-resistance effect element, a GMR element of a meanderingshape is desirable, as shown in the enlarged view of FIG. 13, in which aplurality of belt-like elongated patterns (stripes) are placed in such away that longitudinal directions thereof are parallel with each other bybeing folded back. In the meandering shape, an axial direction (Pindirection) of sensitivity is the direction (widthwise direction of thestripes) perpendicular to a longitudinal direction of a long pattern(longitudinal direction of the stripes). In this meandering shape, theinduced magnetic field is applied in a direction perpendicular to thelongitudinal direction of the stripe (widthwise direction of stripe).

Considering the linearity in the meandering shape, it is desirable thatthe width of the meandering shape in a Pin direction is 1 μm to 10 μm.In this instance, considering the linearity, it is desirable that thelongitudinal direction is perpendicular to the direction of the inducedmagnetic field. With the meandering shape, it is possible to achieve theoutput of the magneto-resistance effect element using fewer terminals(two terminals) than Hall elements.

In addition, an electrode 24 is formed on the aluminum oxide layer 23.The electrode 24 may be formed by photolithography and etching after anelectrode material is formed as a film.

On the aluminum oxide layer 23 formed with the magneto-resistance effectelements 122 a to 122 d and the electrode 24, a polyimide layer 25 isformed as an insulating layer. The polyimide layer 25 may be formed byapplying and curing a polyimide material.

A silicon oxide film 27 is formed on the polyimide layer 25. The siliconoxide film 27 is formed as a film by, for example, a method such assputtering. A polyimide layer 29 is formed on the silicon oxide layer 27as an insulating layer. The polyimide layer 29 may be formed by applyingand curing a polyimide material. Further, the silicon oxide layer 27 andthe polyimide layer 29 can be appropriately omitted.

A magnetic shield 30 is formed on the polyimide layer 29. The materialof the magnetic shield 30 can use a high permeability material such asan amorphous magnetic material, a permalloy-based magnetic material, oran iron-based microcrystalline material. In addition, the magneticshield 30 can be appropriately omitted.

A silicon oxide layer 31 is formed on the polyimide layer 29. Thesilicon oxide layer 31 may be formed as a film by, for example, a methodsuch as sputtering. Contact holes are formed in predetermined regions ofthe polyimide layer 29 and the silicon oxide layer 31 (a region of theelectrode 24), and electrode pads 26 are formed in the contact holes.The contact holes are formed by photolithography and etching. Theelectrode pads 26 may be formed by photolithography and plating afterthe electrode material is formed as a film.

In the magnetic proportional current sensor including theabove-described configuration, as shown in FIG. 14, themagneto-resistance effect element receives the induced magnetic field Agenerated from the current I to be measured to output a voltage inaccordance with the resistance change.

The magnetic proportional current sensor according to the presentinvention includes the magnetic shield 30, as shown in FIG. 14. Themagnetic shield 30 can attenuate the induced magnetic field generatedfrom the current I to be measured and applied to the magneto-resistanceeffect elements. Accordingly, in a case where the induced magnetic fieldA is high, the current measurement can be carried out in a wide range.In addition, the effect of the external magnetic field can be reduced bythe magnetic shield 30.

The magnetic proportional current sensor including the above-describedconfiguration utilizes the magneto-resistance effect element as themagnetic detecting element, in particular, the magnetic field detectingbridge circuit having the GMR element or the TMR element, so that amagnetic proportional current sensor having high sensitivity can beachieved. In addition, in the magnetic proportional current sensor, themagnetic field detecting bridge circuit is constituted of fourmagneto-resistance effect elements with the same film configuration.Further, in the magnetic proportional current sensor including theabove-described configuration, since the magnetic shield 30 and themagnetic field detecting bridge are formed on the same substrate,miniaturization thereof can be achieved. Moreover, since the magneticproportional current sensor does not include the magnetic core,miniaturization and cost reduction can be achieved.

In the magnetic proportional current sensor according to the presentinvention, as shown in FIG. 15, the magnetization directions(magnetization direction of the second ferromagnetic film: Pin2) of theferromagnetic fixed layers of the two magneto-resistance effect elements122 b and 122 d outputting the midpoint potential (Out1) are differentfrom each other by 180° (antiparallel), and the magnetization directions(magnetization direction of the second ferromagnetic film: Pin2) of theferromagnetic fixed layers of the two magneto-resistance effect elements122 a and 122 c outputting the midpoint potential (Out2) are differentfrom each other by 180° (antiparallel). In addition, the resistancechange rate of the four magneto-resistance effect elements 122 a to 122d is equal to each other. In a case where the angle of the magneticfield applied to the ferromagnetic fixed layer is equal, it is desirablethat the magneto-resistance effect elements 122 a to 122 d represent thesame resistance change rate at the same magnetic strength.

In the magnetic proportional current sensor including the fourmagneto-resistance effect elements 122 a to 122 d placed as describedabove, the current to be measured is measured by the voltage differencebetween two outputs (Out1 and Out2) of the magnetic field detectingbridge circuit 13.

As shown in FIG. 15, if the current to be measured flows in thedirection of the arrow, the induced magnetic field A is respectivelyapplied to the four magneto-resistance effect elements 122 a to 122 d.In the magnetic field detecting bridge circuit 13, the resistance valuesof the magneto-resistance effect elements 122 a to 122 d in a zeromagnetic field are equal to each other (Rcom). In addition, theresistance change rates of the magneto-resistance effect elements 122 ato 122 d are equal to each other. The output between themagneto-resistance effect elements 122 b and 122 d is set to Out1, andthe output between the magneto-resistance effect elements 122 a and 122c is set to Out2. Moreover, a resistance value of the magneto-resistanceeffect element 122 b is set to R1, a resistance value of themagneto-resistance effect element 122 c is set to R2, a resistance valueof the magneto-resistance effect element 122 d is set to R3, and aresistance value of the magneto-resistance effect element 122 a is setto R4.

When the resistance change amount of the magneto-resistance effectelements 122 a to 122 d according to the induced magnetic fieldgenerated from the current I to be measured is ΔR, a midpoint potentialdifference (Out1 and Out2) of the bridge is obtained as follows:

Resistance between Vdd and Gnd1=

(R1−ΔR)+(R3+ΔR)=R1+R3=2×R _(com)

Resistance between Vdd and Gnd2=

(R2+ΔR)+(R4−ΔR)=R2+R4=2×R _(com)

Potential of Out1=(R3+ΔR)/(R1+R3)×Vdd

=(R _(com) +ΔR)/(2×XR _(com))×Vdd

Potential of Out2=(R4−ΔR)/(R2+R4)×Vdd

=(R _(com) −ΔR)/(2×R _(com))×Vdd

Potential difference between Out1 and Out2=

(2×ΔR)/(2×R _(com))×Vdd

=ΔR/R _(com) ×Vdd

As described above, in the magnetic proportional current sensorincluding the magnetic detecting bridge circuit according to the presentinvention, a term ΔR is not contained in a denominator in the equationof the bridge midpoint potential difference for obtaining the potentialdifference between Out1 and Out2. For this reason, the output of themidpoint potential difference is varied in proportion to the inducedmagnetic field which is generated by the current I to be measured. As aresult, it is possible to carry out the current measurement with a highdegree of accuracy. In addition, since the wiring pattern is symmetricalto the power supply point, there is no difference in the wiringresistances at both sides of the power supply point. As a result, sincethere is no misalignment of the midpoint potential caused by thedifference in wiring resistances, it is possible to carry out thecurrent measurement with a high degree of accuracy. The presentinvention is particularly useful in a magnetic proportional currentsensor.

FIGS. 10A to 10C and FIGS. 11A and 11C are diagrams illustrating amethod of manufacturing the magneto-resistance effect element in thecurrent sensor according to an embodiment of the present invention.First, as shown in FIG. 10A, the seed layer 42 a, the firstferromagnetic film 43 a, the antiparallel coupling film 44 a, the secondferromagnetic film 45 a, the non-magnetic intermediate layer 46 a, thesoft magnetic free layers (free magnetic layer) 47 a and 48 a, and theprotective layer 49 a are sequentially formed on the substrate 41.During film formation of the first ferromagnetic film 43 a and thesecond ferromagnetic film 45 a, the magnetic field is applied to thefirst ferromagnetic film and the second ferromagnetic film in thewidthwise direction of the stripes of the meandering shape. In FIGS. 10Ato 10C, the applying direction of the magnetic field for the firstferromagnetic film 43 a is a direction facing a front side from a frontsurface of the paper, and the applying direction of the magnetic fieldfor the second ferromagnetic film 45 a is a direction facing a lateralside from the front surface of the paper. During film formation of thesoft magnetic free layers (free magnetic layer) 47 a and 48 a, themagnetic field is applied to the soft magnetic free layers in thelongitudinal direction of the stripes of the meandering shape.

Next, as shown on FIG. 10B, a resistor layer 50 is formed on theprotective layer 49 a, and then the resistor layer 50 is left on theregion of the magneto-resistance effect element 122 a side byphotolithography and etching. Then, as shown in FIG. 10C, the exposedstacked film is removed by ion milling or the like to expose a region ofthe substrate 41 in which the magneto-resistance effect element 122 b isprovided.

Then, as shown in FIG. 11A, a seed layer 42 b, a first ferromagneticfilm 43 b, an antiparallel coupling film 44 b, a second ferromagneticfilm 45 b, a non-magnetic intermediate layer 46 b, soft magnetic freelayers (free magnetic layer) 47 b and 48 b, and a protective layer 49 bare sequentially formed on the exposed substrate 41. During filmformation of the first ferromagnetic film 43 b and the secondferromagnetic film 45 b, the magnetic field is applied to the firstferromagnetic film and the second ferromagnetic film in the widthwisedirection of the stripes of the meandering shape. In FIGS. 11A to 11C,the applying direction of the magnetic field for the first ferromagneticfilm 43 b is a direction facing a front side from a front surface of thepaper, and the applying direction of the magnetic field for the secondferromagnetic film 45 b is a direction facing a lateral side from thefront surface of the paper. During film formation of the soft magneticfree layers (free magnetic layer) 47 b and 48 b, the magnetic field isapplied to the soft magnetic free layers in the longitudinal directionof the stripes of the meandering shape.

Next, as shown on FIG. 11B, a resistor layer 50 is formed on theprotective layers 49 a and 49 b, and then the resistor layer 50 isremained on the formation region of the magneto-resistance effectelements 122 a to 122 d by photolithography and etching. Then, as shownin FIG. 11C, the exposed stacked film is removed by ion milling or thelike to form the magneto-resistance effect elements 122 a to 122 d.

As described above, with the current sensor according to the presentinvention, since the magnetization directions of the self-pinned typeferromagnetic fixed layers in the two magneto-resistance effect elementsoutputting the midpoint potential are different from each other by 180°,the output of the midpoint potential difference is changed in proportionto the induced magnetic field which is generated from the current to bemeasured in the magnetic detecting bridge circuit. In addition, there isno difference in the wiring resistances in the magnetic detecting bridgecircuit, and it is possible to carry out the current measurement with ahigh degree of accuracy.

The present invention is not limited to the embodiments, but may bevariously modified. For example, the material, the connected relation ofeach element, the thickness, the size, and the manufacturing method inthe embodiments may be variously modified. In addition, the presentinvention may be variously modified without departing from the scope ofthe invention.

The present invention can be applied to a current sensor for detectingthe intensity of a current to drive a motor of an electric vehicle.

It should be understood by those skilled in the art that variousmodifications, combinations, sub-combinations and alterations may occurdepending on design requirements and other factors insofar as they arewithin the scope of the appended claims or the equivalents thereof.

1. A current sensor comprising: a magnetic detecting bridge circuitwhich is constituted of four magneto-resistance effect elements with aresistance value varied by application of an induced magnetic field froma current to be measured, and has an output between twomagneto-resistance effect elements, wherein the four magneto-resistanceeffect elements have the same resistance change rate, and include aself-pinned type ferromagnetic fixed layer which is formed byanti-ferromagnetic ally coupling a first ferromagnetic film and a secondferromagnetic film via an antiparallel coupling film therebetween, anonmagnetic intermediate layer, and a soft magnetic free layer,magnetization directions of the ferromagnetic fixed layers of the twomagneto-resistance effect elements providing the output are differentfrom each other by 180°, and the magnetic detecting bridge circuit haswiring symmetrical to a power supply point.
 2. The current sensoraccording to claim 1, further comprising: a feedback coil which isplaced in the vicinity of the magneto-resistance effect element, andgenerates a cancelling magnetic field for cancelling the inducedmagnetic field; and a magnetic shield which attenuates the inducedmagnetic field and enhances the cancelling magnetic field, wherein thecurrent to be measured is measured based on a current flowing in thefeedback coil at the time of an equilibrium state in which the inducedmagnetic field and the cancelling magnetic field are cancelled byenergizing the feedback coil with a voltage difference obtained from themagnetic detecting bridge circuit.
 3. The current sensor according toclaim 2, wherein in the four magneto-resistance effect elements, aplurality of belt-like elongated patterns are placed in such a way thatlongitudinal directions thereof are parallel with each other by foldingback the elongated pattern, and the induced magnetic field and thecancelling magnetic field are applied in a direction perpendicular tothe longitudinal direction.
 4. The current sensor according to claim 1,wherein the magnetic detecting bridge circuit measures the current to bemeasured by the outputs of the four magneto-resistance effect elementswhich are in proportion to the induced magnetic field.
 5. The currentsensor according to claim 1, wherein the first ferromagnetic film ismade of a CoFe alloy containing Fe of 40 atomic percent to 80 atomicpercent, and the second ferromagnetic film is made of a CoFe alloycontaining Fe of 0 atomic percent to 40 atomic percent.
 6. The currentsensor according to claim 1, wherein the magnetic shield is made of ahigh permeability material selected from a group consisting of anamorphous magnetic material, a permalloy-based magnetic material, and aniron-based microcrystalline material.